Field of the Invention
The present invention concerns a refrigeration installation and method.
The invention concerns in particular a low-temperature refrigeration installation and method wherein a gas with a low molar mass (for example hydrogen or helium) is used as a refrigerating fluid in order to attain very low refrigeration temperatures (for example 4.5 K for helium). Obtaining refrigeration at temperatures of 30 K and lower generally requires the use of a refrigerant such as helium. The helium is compressed at a hot end of the loop or circuit, and then cooled and expanded in the cold part of the loop (cold box). The major part of the refrigerant is heated by exchange and recycled in the compression stage. In some applications, part of the working gas may be liquefied.
Related Art
The compression of the helium liquefaction/refrigeration cycles generally uses one or more stages of compression machines (compressors) with lubricated screws followed by an oil-separation system.
If it is necessary to have several refrigerators, each refrigerator is connected to its own compression station. According to the rates required, each compression level may be divided into several compressors in parallel. The primary oil-management and cooling systems may be common to several compressors or be dedicated to each one.
After the compression and oil separation thereof the low molecular mass gas is cooled and expanded in cryogenic expansion turbines of a cold box in order to attain the required temperature level. The cold not used by the user of the refrigerator/liquefier is then transmitted to the working fluid at high pressure in order to cool it in the heat exchangers. The working gas at low and medium pressure of the circuit returns to the intake of the compressors.
For large refrigeration systems, for example greater than 20 kW, equivalent to 4.5 K, it is necessary to use several separate refrigerators in parallel connected to the same application to be cooled. The fluctuating thermal loads of the application to be cooled cause fluctuations in output on the compressors of the compression station. The costs of the compression station (equipment, integration and installation) are relatively high compared with the total cost of the installation.
The refrigeration cycles (which generate the cold) are conventionally “closed” at each refrigerator. That is to say the cycle output of working fluid that enters the cold box stems mainly from this same cold box. On the other hand, these cycle outputs are “open” or combined at the application to be cooled (the working fluid output supplied by the refrigerators is shared for the application to be cooled and then returns to each refrigerator through a respective distribution system).